This invention relates to voltage controlled crystal oscillators and, more particularly, to a voltage controlled crystal oscillator that is useful in the circuitry of a television system.
Crystal controlled voltage controlled oscillators are widely used in television chroma systems for the regeneration of the color signal subcarrier. It is particularly desirable, from a manufacturing standpoint, to reduce as much as possible of such a system to integrated circuits. In the past, others have proposed crystal tuned voltage controlled oscillators which allow great portions of the circuit to be manufactured in integrated circuit form. One such oscillator is disclosed in U.S. Pat. No. 3,973,221, which was issued to William B. Jet, Jr., and is assigned to the same assignee as the present invention. However, the present invention permits yet a greater portion of the circuit to be in integrated circuit form. The above mentioned U.S. Pat. No. 3,973,221, is hereby incorporated herein by reference.
Accordingly, an object of the present invention is to provide an improved voltage controlled crystal oscillator.
Another object of the present invention is to provide an integrated circuit oscillator having phase shifting capacitors which can be diffused as a portion of the integrated circuit.
Yet another object of the invention is to provide an improved voltage controlled crystal oscillator which does not oscillate at third overtones of the crystal frequency and yet does not require discrete phase shifting components.
A further object of the present invention is to provide a voltage controlled crystal oscillator, which can be entirely fabricated in monolithic integrated circuit form, except for the crystal.